Generally, portable electronic appliances, such as mobile phones, personal digital assistants (PDAs), notebook computers, liquid crystal display televisions (LCD TVs), portable wireless transceivers, CD players, and MP3 players, are freely and conveniently used by users without being limited with respect to location, so that the portable electronic appliances have been widely and preferably used in recent years.
However, the portable electronic appliances discharge a great quantity of harmful electromagnetic waves due to the variety of electromagnetic circuit units installed therein, and most harmful electromagnetic waves discharged from the appliances are absorbed by the bodies of the users while the users carry the appliances, thus being injurious to health.
The casings of the conventional portable electronic appliances are preferably produced using materials prepared by adding conductive coating materials, additives or fillers to polymer materials.
To prevent harmful electromagnetic waves of internal electromagnetic circuit units of portable terminals from leaking outside the casings of the terminals, the conventional casings for the portable terminals made using the polymer materials are coated with conductive coating materials on the inner and outer surfaces thereof, thus having electric conductivity higher than a predetermined level.
In a conventional conductive coating process, to provide conductivity to polymer materials, a variety of additives or fillers may be added to the polymer materials of the casings of the portable electronic appliances. Examples of the fillers are powdered carbon, carbon fibers, and metallic materials, such as powdered silver.
Conventional fillers, such as powdered carbon or carbon fibers, which are added to the polymer materials in the related art have insufficient volume and a resistance lower than 10Ω/□. The metallic material, such as powdered silver, forms a layer on the surface of the casing, thus degrading the quality of the casing. Furthermore, the metallic material must be added to the polymer material of the casing in an amount up to 60%, so that the metallic material cannot be preferably used, due to the weight, quality, physical and chemical performance, and cost.
Furthermore, the casings for the portable terminals, produced using the above-mentioned metallic materials for shielding electromagnetic waves, are not easily recycled. To recycle the conventional casings, expensive sorters must be used, thus increasing the cost of recycling the casings.
Particularly, the casings of the electronic appliances, which are produced using polymer materials having the conductive coating materials, such as powdered silver or powdered carbon, have reduced durability due to physical and chemical factors, so that the surfaces of the casings may be discolored, easily scratched, or easily worn, thus reducing the expected life spans of the electronic appliances.
Further, the conventional display units of the electronic appliances are made of nonconductive materials, so that it is almost impossible using conventional techniques to prevent the leakage of electromagnetic waves through the display units or to prevent the display units from being charged.
If the coated conductive layer of an electronic product manufactured using a polymer material and a molding process does not have uniform thickness, the coated conductive layer cannot provide a desired coating effect. Thus, to form a coated conductive layer having uniform thickness on an electronic product, a complex and precise high technique and complex and precise expensive equipment must be used. Therefore, the construction of the processing equipment becomes complicated and the processing technique must be precise, so that the production cost of the products is increased due to the cost of developing and designing the processing equipment and the processing techniques.
To accomplish a desired effect of shielding electromagnetic waves and to provide desired conditions for maintaining the stable and reliable operation of the internal circuit units of the electronic appliances, it is necessary to maintain a predetermined shielding ratio, for example, a 20% shielding ratio, at uniform distribution. However, it is almost impossible to accomplish such a shielding ratio using conventional techniques due to technical limits.
Furthermore, because the conventional electric appliances made of polymer materials using expensive additives are not easily recycled, the production cost of the appliances is increased. Due to insufficient performance of the appliances with respect to shielding of electromagnetic waves or the prevention of electric charges, liability for malfunctions of the appliances is increased, thus imposing a heavy burden on the manufacturers. Furthermore, the insufficient performance of the appliances in the shielding of electromagnetic waves or the prevention of electric charges prevents the appliances from being easily recycled.